Regeneratable air conditioning systems provide the possibility of recouping some of the energy of the return or exhaust air which has just previously circulated in an interior space as a cooled and humidity conditioned air. It is known, for example, to pass such exhaust air through a heater to increase its temperature and to decrease its humidity content and to thereafter pass the exhaust air into contact with a desiccant type humidity removal device which conditions the process or supply air. In one type of desiccant device, a desiccant wheel is rotated through a regeneration zone in which heated exhaust air removes moisture from the portion of the wheel in the regeneration zone to thereby restore that wheel portion for subsequent moisture pick up from the supply air.
Additionally, it is known to draw outside air which has not circulated in the interior space into an air conditioning system to assist in the latent heat or the sensible heat removal operations. Although such outside air may have a higher enthalpy or heat content than the exhaust air and, thus, have correspondingly less capacity for cooling the heat removal elements, such air does not bring with it one drawback of the exhaust air--namely, the drawback that the energy recoupment of exhaust air may promote the growth of detrimental bacteria such as legionella pneumophila which causes legionnaires' disease and Pontiac fever.
It has been suggested to utilize both exhaust air and outside air for regeneration purposes. For example, U.S. Pat. No. 5,170,633 to Kaplan discloses an air conditioning system having two desiccant wheels and evaporative coolers with regeneration being partially provided by waste or exhaust heat. However, the contamination risk noted with respect to the exhaust air is not specifically addressed by Kaplan.
Thus, the need exists for an air conditioning system which maximizes the recoupment of exhaust air energy and additionally utilizes the energy of outside air while minimizing contamination risks. Moreover, such an improved air conditioning system could reduce the operating cost of conditioning the air if the removal of latent heat is assisted without a commensurate increase in energy requirements for removing sensible heat.
However, in view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in this art how an improved air conditioning system could be provided.